In recent years, backhoes have become very popular implements in the construction trade for digging all types of minor excavations which do not warrant the moving of a conventional shovel-type digger or dragline to the working area. Additionally, such backhoe assemblies are normally carried on the rear portion of a farm or industrial tractor and the tractor is available for other uses, for example, a dozer blade or a front end loader may be mounted on the forward portions of the tractor.
Despite the obvious need for the operator to know at all times the effective depth of the excavation that he is producing, prior to this invention there have been no reliable instruments provided for continuously indicating to the operator the effective digging depth of the teeth of the backhoe bucket. The absence of such an indicating system is understandable when one considers that the depth of such digging teeth is determined by a plurality of variables, namely, the angle of the outreach boom relative to the vehicle or the horizontal, the angle of the downreach boom relative to the outreach boom, and the angle of the bucket relative to the downreach boom. As a practical matter, for the bucket teeth to move horizontally at a constant depth, at least two (2) of said angles must be concurrently varied. Furthermore, in some excavations, such for example as required for installation of sewer or drain lines, the absolute depth of the excavation must be precisely determined and, prior to the development of this invention, such absolute depth could only be determined by inserting an elongated surveyors rod into the trench and measuring the depth by conventional, yet time consuming, surveying techniques.